Mesh networking is a way to route data and instructions between nodes. A node can be any device connected to a computer network. Nodes can be computers, routers, or various other networked devices. On a TCP/IP network, a node is any device with an Internet Protocol (IP) address. Mesh networking allows for continuous connections and reconfiguration around broken or blocked paths by “hopping” from node to node until the destination is reached. Mesh networks differ from other networks in that the component parts can all connect to each other via multiple hops, and they generally are not mobile devices. In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate node in a network to another node in the network. On the Internet (or a network that uses TCP/IP), the number of hops a packet has taken toward its destination (called the “hop count”) is kept in the packet header.
Wireless mesh networks employ intelligent nodes typically including a wireless (e.g. radio) transmitter and receiver, a power source, input devices, sometimes output devices, and an intelligent controller, such as a programmable microprocessor controller with memory. In the past, wireless mesh networks have been developed having configurations or networks for communication that are static, dynamic or a hybrid of static and dynamic. Power for these networks has been supplied either via wires (the nodes are “plugged in”) or from batteries in each node. As the size, power, and cost of the computation and communication requirements of these devices has decreased over time, battery-powered wireless nodes have gotten smaller; yet, the computing demands on the wireless nodes have increased.
Wireless mesh network technology can be used for deploying sensors as nodes in a variety of different environments for monitoring diverse parameters such as, for example, temperature, pressure, and humidity. These types of networks can be denoted wireless sensor networks (WSN). Each sensor in a WSN is typically powered by a battery and therefore has a limited energy supply and operational capability. Because the sensors are constantly monitoring the environment and communicating with other nodes, it is important to efficiently manage the power consumed by each sensor. Further, it is important to monitor the operational status of each of the sensors.
Given that most WSN devices are battery powered, the overall network lifetime depends on the efficiency with which sensing, computing, and data transmission by the sensors can be achieved. Because the power requirements for wireless communication by the sensors are orders of magnitude higher than the other sensor operations, it is critical that operation of the radios on these devices be managed carefully. This is primarily achieved by turning the radio on only when devices need to send and/or receive data. The operational lifetime of the network, thus, depends on the ability to identify and schedule wakeup and sleep times for the radios in the wireless network nodes.
Time division multiple access (TDMA) is a well-known channel access method for shared medium (usually radio) networks. TDMA allows several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his/her own timeslot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only the part of the available bandwidth. The timeslot definition and allocation in TDMA, however is usually determined globally for all nodes. It is therefore harder to modify the timeslot definition and allocation in TDMA if the network configuration or communication requirements change.
In CSMA/CA (Carrier Sense Multiple Access With Collision Avoidance), a station that wants to transmit a packet first listens to the shared channel for a predetermined amount of time to determine if the channel is busy or not. If the channel is sensed idle, then the station is allowed to transmit. If the channel is busy, the station defers its transmission. Once the channel is clear, a station sends a short signal telling all other stations not to transmit, and then sends its packet. In Ethernet 802.11, the station continues to wait for a random amount of time (to reduce the probability of collision), and checks to see if the channel is still free. If it is free, the station transmits, and waits for an acknowledgment signal that the packet was received. CSMA/CA is used where collision detection cannot be implemented due to the nature of the channel. CSMA/CA is typically used in 802.11 based wireless local area networks (LAN's); because, it is not possible to listen to the channel while sending. Therefore, collision detection is not possible. Another reason is the hidden terminal problem, where node A, in range of the receiver R, is not in range of another node B, and therefore cannot know if B is transmitting to R.
In Asynchronous Transfer Mode (ATM) systems, a fixed-size data cell is transmitted in a channel-specific time period of fixed duration during which a unit of communication occurs between two fixed terminals without conflict. The motivation for the use of small data cells in ATM networks was the reduction of jitter (delay variance, in this case) in the multiplexing of data streams. The reduction of jitter (and also end-to-end round-trip delays) is particularly important when carrying voice traffic. Again however, the cell definition and communication in ATM is fixed and non-adaptable.
U.S. Pat. No. 5,896,412 describes a method of wireless communication among a plurality of stations in which each station communicates with all of the other stations over a cycle time divided into a plurality of communication sectors during each of which one of the stations transmits, including the step of changing the frequency of the transmission in accordance with a predetermined protocol, only at the end of a sector in which one of the stations transmits. Preferably, the frequency of transmission is reset to a given frequency in accordance with the protocol when none of the stations transmit over a predetermined period.
U.S. Patent Application No. 20060029061 describes a packet communication network, in which packet switched transport is provided among intelligent nodes wherein the duty cycling of the intelligent nodes is minimized in order to maximize power life using a synchronization algorithm that assures all nodes are able to propagate information through the network without undue use of transmission and reception power. Frequency hopping time-division multiple access supports packet communication between intelligent nodes via assigned directed links, each link being assigned to a time-channel offset (cell) in a superframe, so that a link carrying a packet string between any two intelligent nodes is active only during its assigned time slot.
Thus, an apparatus and method for adaptive data packet scheduling in a mesh network are needed.